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Thanks for the scientific insight Richard. I haven't dived Whitefish Point for a couple of years, but was impressed with the lack of zebra mussels there in 1999. Given that upbound and downbound freighter traffic is heavily concentrated there (hence the many wrecks) I was pleased to see not a single living zeeb. A park ranger at Isle Royale told me a couple weeks ago that there were a few zeebs spotted at Windigo (west end of island) but nothing too worrisome. Lake Superior holds the secret to knock off these pests, and hopefully guys like you will figure that out. MJB --- Richard Hayward <hddiver@sy*.ca*> wrote: > > Hi my name is Richard Hayward, I have been on the list for about 6 years > have posted a few times, I am originally from Sault Ste. Marie but now live > in St. Louis (The techdiving scene is non existent in the midwest. Bonne > Terre mines could have potential but they only give guided tours there at a > cost of 130$ for two air or nitrox dives yikes! everything else is quarries > unless someone can guide me to something better please!), and have dove > Whitefish point and the Straights of Mackinaw tons and also am a well > traveled commercial diver. > > Presently I work with an ecological firm called Ecological Specialists Inc. > as the scientific diving co-ordinator. I am not a malacologist (specializing > in mussels) but work directly with two very well respected malacologists > Heidi Dunn and Charles Howard. Ecological Specialist Inc. is located in the > midwest specializing primarily in freshwater mussels among other things. My > job is the identification of North American freshwater mussels for the > purpose of estimating population densities, identifying endangered species, > relocation, also for conducting dives per OSHA and USACE regulations plus > many other objectives depending upon the client. It is not scuba, all > surface supplied to answer the curious. > > The ability for a zebra mussel to survive depends on several factors > including: > > 1) Temperature > 2) Dissolved Oxygen > 3) PH level > 4) Calcium levels > 5) Salinity levels > 6) Water Velocity > 7) Turbidity > 8) Substrate condition > > The most important of these factors is temperature, calcium levels and PH. > > Temperature - > > "Temperature plays an important role in the seasonal life cycle and > physiology of the zebra mussel. Particular temperature regimes cue major > life cycle events such as reproduction and larval development. Zebra mussel > spawning (release of gametes into the water column) will not occur at > temperatures below 10 - 16 degrees C for either North American (Herber et > al. 1989, Griffiths et al. 1991, Claudi and Mackie 1994) or European > (Kornobis 1977, Stanczykowska 1977, Walz 1978, Borcherding 1991, Sprung > 1991) populations. Garton and Hagg (1993) report a threshold of 18 degrees C > for spawning in southwester Lake Erie. Thew water temperature ranges > coincide with June - September in most of the the North American temperate > freshwater systems. As temperatures decline in the fall, zebra mussels begin > gamtonesis while good supplies are still adequate... > > Temperature also has a significant effect on zebra mussel growth. The term > growth is used to describe the accumalation of somatic body tissue. Shell > growth will not occur at temperatures below 3 degrees C (Smit et al. 1992). > Temperatures as low as 6 degrees C (Bij da Vaate 1991)... Claudi and Mackie > (1994) report a growth range of 8 - 10 degrees C for Lake St. Clair mussel > populations. > > Temperature plays a significant role in the survival success of zebra > mussels. It is on of the factors that may play a role in limiting the > distribution of the animal. However it is important to realize that once the > animals become acclimatized to warmer habitats, the upper thermal tolerances > could shift over several years. Although they can survive temperatures > slightly in excess of 30 degrees C for short periods, optimum temperatures > are 0 - 25 degrees C. > > Values used for determining risk for temperature by the risk assessment > calculator are as follows; > If the number of months above 12 degrees C is > less than 1 - slim to none > 1 to 3.999999 - moderate > 4 or greater - high " Zebra Mussel information System version 3.0 > > Here is a link to current lake superior temperature as of today August 25 > 2001 it appears to be on average about 12 degrees C > http://www.coastwatch.msu.edu/superior/s32.html or > http://coastwatch.glerl.noaa.gov/cwdata/lct/glsea.gif which is close to the > right temperature for reproduction but is only that warm for very short > periods of the year and it does not appear that it is in the ideal > temperature range long enough to support reproduction. The hot spots MJB > talks about in Lake Superior also get the warmest during the summer if you > look at temperature histories at these links. > > > Calcium Levels - > "Calcium (Ca) is a necessary element in the composition of the bivalve > shell. Sprung (1987) reported that 40 - 55 mg of Ca per liter was sufficient > for larval development and that a minimum of 24 mg Ca per liter was > necessary for 10% larval survival. Stanczykowska (1977) found calcium from > 28 - 109 mg Ca per liter in lakes with successful zebra mussel populations. > > Zebra mussels do not survive to any great extent when there is insufficient > calcium levels. Calcium is a necessary component for shell secretion and > formation. > > The following table (taken from Claudi and Mackie (1994)) illustrate the > growth and survival of zebra mussel from waters with varying calcium levles. > > Growth and survival Calcium range mg/l > no survival 5 to 6 > poor growth 10 to 11 > Moderate growth 25 to 26 > Good growth 35 to >35 > > Values used for determining risk for calcium values by risk assessment > calculator are as follows > less than 20.999999 - slim to none > 21 - 54.999999 - moderate > greater than 55 - high " Zebra Mussel information System version 3.0 > > PH - > "The pH of a body of water will play a role in determining zebra mussel > success. pH lower than 7.4 will inhibit zebra mussel larval development > (sprung 1987). Kornobis (1977) reports pH from 7.2-8.7 as having little > effect on veliger densities in the phytoplankton. Other authors (Dries and > Theede 1974 as referenced by Sprung 1992) reported that survival of bivalves > was higher at pH values between 7.0 and 7.5 Stanczykowska (1977) reported > zebra mussels in lakes with hypoimnetic pH values from 6.6 - 8.0 and > epilimnetic values from 8.5 - 7.7. > > The amount of hydrogen ions in the water or the pH can significantly impact > aquatic life. Bivalve molluscs, such as zebra mussels, are at risk at either > extreme of the pH scale (i.e., below 6 and above 9). > > The following table (taken from Claudi and Mackie (1994)) illustrates the > survival and growth potential of zebra mussels from waters with different pH > values. > > Growth and survival pH range > no survival 0 - 6.8 > poor growth 6.9 to 7.4 > moderate growth 7.5 to 7.8 > good growth 7.9 to 8.0 > best growth >8.0 > > Note how there is no upper survival limit for the best growth which is > contrary to other published information where the incipient lethal larval > level is around 7.4. Apparently, there are different thresholds for both > immatures and adult growth. > > Values used for determining risk for pH values by the risk assessment > calculator are as follows > 0 to 6.7999999 - slim to none > 6.8 to 7.39999999 - moderate > 7.4 to 8.999999 - high > 9 to 10 - slim to none" Zebra Mussel information System version 3.0 > > > > Water quality also suggests a very low calcium level of 5.9 mg/l reported at > one station which is directly related to shell production other stations > also reported some low calcium levels. Data available at this link > http://oaspub.epa.gov/storpubl/legacy/proc_generate_next and that pH is also > marginally condusive as well relating to poor growth. > > If you were to put all of these factors together, not just one on its own, > they are probably what is keeping zebras from invading Lake Superior. > > The international joint commission also has lots of resources available at > this link http://www.ijc.org/ijcweb-e.html > > I can do much more research to this fact as I have a lot of professional > resources at my fingertips. > > Keep diving everyone, because now that I am in the midwest I miss the good > times. > > Also the wreck diving in the great lakes is amazing especially whitefish and > the straights of mackinaw, to say they are the best in the world though is a > bold statement. I would definately say that they are one of the best spots > in the world, for number and quality of wrecks, whitefish is deep but > amazing, the straights however offer very nice wrecks and most of them under > 100 feet means you can take you whole family there which is nice. The thing > to remember when diving in the Great Lakes is the distance to a half decent > chamber and someone competent in hyperbaric medicine. Just make sure you > have your DAN insurance. > > > Dive safe configure right. > Richard Hayward > > > -----Original Message----- > From: Michael J. Black [mailto:mjblackmd@ya*.co*] > Sent: Saturday, August 25, 2001 9:01 PM > To: Aquanaut Mail > Subject: Zebra Mussels > > > Lake Superior not only has some of the best wreck diving in the world, > it has very few zebra mussels compared to the other Great Lakes. Anyone > wanna give a good explanation as to why this is? And before you say that > the water is "too clean" or "too cold," consider that even the scientists > don't know, but the low Calcium levels in the water may be part of the > reason for the inability of zeebs to thrive in Superior. I have seen > shallow wrecks (less than 60 ffw) in Lake Michigan become smothered with > zeebs, beginning around 1995, obscurring engine details to the point of > making the wrecks undesirable to dive. Deeper wrecks are relatively spared, > but even depth doesn't stop zeebs or their relatives (Quagga mussels) from > latching on. Improved visibility from these filter feeders is often > exaggerated by divers, but there is no question that water clarity has > improved wherever zeebs have taken hold, some consolation. > === message truncated === __________________________________________________ Do You Yahoo!? Make international calls for as low as $.04/minute with Yahoo! 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